cm: Add proper readme

cm/README.md

@@ -1,26 +1,68 @@
-# Cookie Monster #
+# Cookie Monster (aka cm)
 
 This sublibrary (someday perhaps available separately, but for now, not) is
-convenience wrapper for handling client state in client (fully in the
-cookie). For now, the state is not encrypted at all (although we could), as
-I do not really see the point. The idea is not to store secrets using this,
-just e.g. state in various views so that the client resumes same state
+convenience wrapper for handling client state in server (fully in the
+cookie).
+
+For now, the state is not encrypted at all (although we could), as I do not
+really see the point. The idea is not to store secrets using this, just
+e.g. state in various views so that the client resumes same state
 implicitly when they go back to a view.
 
+
 ## Short form
 
+Define state as normal struct, e.g.
+
 ```
-err = monster.Run(r, w, &state)
+type State struct {
+  Number int `json:"n" cm:"number"`
+}
 ```
 
-Where
+and then call
+
 ```
-r = http.Request
-w = http.ResponseWriter
-state = arbitrary struct (ideally empty)
+err = cm.Run(r, w, &state)
 ```
 
+Where
+- `r`: `http.Request`
+- `w`: `http.ResponseWriter`
+- `state`: arbitrary struct with cm + json tags (ideally empty but this will clear most of the state)
+
 The struct is examined through reflection and `cm:"field"` entries are
-CRUDed based on `"field"` in the `http.Request`. Note that json definitions
-must be also supplied for the fields, or otherwise they will not be
-imported/exported.
+CRUDed based on `"field"` in the `http.Request.Form`. They are persisted
+automagically to cookie derived from the struct name, and with the `json`
+tagged names (preferably short ones, as cookie space is limited). If json
+definitions are not supplied, they will not be imported/exported.
+
+## Supported datatypes
+
+Currently the code supports only following datatypes:
+
+- bool
+- int*
+- string
+- uint*
+
+Other types, if tagged, cause an error.
+
+## What does it do?
+
+The above cm.Run call will:
+
+- read existing json cookie with name `cm.<module>.State` and unmarshal
+  JSON content from it to the State struct
+- reads query parameter 'number', and if it is set, update `state` instance
+- (.. same with other fields too, if any ..)
+- if any of the fields were updated, set the updated cookie for the
+  response
+
+## TODO
+
+- Perhaps make the configuration also accept Path? For now, cookies are
+  scoped to Path "/" so e.g. global state can be used to convey them; this
+  may not be optimal always.
+
+- Document this better?